Anesthetic preparations



Patented July 22, 1941 ANESTHETIC' PREPARATIONS Robert R. Burtner, Niles Center, 111., assignor to G. D. Searle & 00., a corporation of Illinois No Drawing. Application March 17, 1938, Serial No. 196,542

7 Claims.

My invention relates to the production of dialkylaminoalkanol esters of carbazole 2, 3 or 4 carboxylic acids which possess the general formula:

where R is H, methyl, ethyl, propyl, butyl, amyl or benzyl R is methyl, ethyl, propyl, butyl, amyl or benzyl n is an integer from 1 to 4 (the chain being either straight or branched) R is H, NH2, OH or OR. (B being methyl, ethyl,

propyl, butyl, amyl or benzyl) and. may be attached to any carbon of the carbazole nucleus not already substituted by the carboxyl group.

These esters may be used in the form of their free bases or of their salts with organic or inorganic acids or with complexes such as the borates.

General methods of synthesis of compound of this series The acid chloride of a carbazole carboxylic acid or of a substituted carbazole carboxylic acid is treated with one equivalent of the desired dialkylaminoalkanol in an inert solvent such as benzene. The mixture is heated for a short time to insure completion of the reaction. The reaction mixture is shaken with dilute hydrochloric acid, causing the hydrochloride of the dialkylaminoalkanol carbazole carboxylate to dissolve in the aqueous phase. By making this aqueous solution alkaline with sodium hydroxide, the free base precipitates. It is separated, and dissolved in ether or acetone, which solution is then treated with an excess of dry hydrogen chloride. The resulting precipitate is then crystallized from a suitable solvent.

If an aminocarbazole carboxylic acid derivative is desired, the corresponding nitrocarbazole carboxylic acid chloride is used at the beginning and the aqueous solution obtained above by shaking with dilute hydrochloride acid is directly reduced with such reagents as, for example, tin and bydrochloric acid and is then worked up in the usual way.

Those compounds with OH or R as substituents are prepared by starting with the acid chloride of the appropriately substituted carbazole carboxylic acid, and by then proceeding in substantially the same manner.

These derivatives, either substituted or unsubstituted, constitute a new class of anesthetics. The effect of the substitutions is to increase or in some cases decrease the efficacy as compared to the unsubstituted compounds and may also affeet the toxicity, either favorably or adversely. However, for illustratiomthe properties of the three simplest compounds may be compared with the well-known local anesthetic, cocaine. In these examples, the first figure gives the toxicity, using cocaine as a reference, and the second gives the duration of anesthesia of the rabbits cornea, in minutes:

Cocaine-1.0045 minutes using a 1% solution; hydrochloride of diethylaminoethanol carbazole- 2-carboxylate-L00-87 minutes using a 1% solution; hydrochloride of diethylaminoethanol carbazole-3-carboxylate-0.38-16 minutes using a 0.1% solution; hydrochloride of diethylaminoethanol carbazole-4-carboxy1ate0.08-8 minutes using a' 1% solution.

These esters are anesthetic either as the free bases or as the salts with organic or inorganic acids. Moreover, they form water-soluble, anesthetic complexes with metaboric acid, in the same fashion as 'do procaine and other compounds of the same type. Such salts and complexes modify the time required for onset of anesthesia, as well as the length of its duration. They are useful from a solubility standpoint as, by appropriate selection of acid group, the solubility in water or in non-aqueous solvents may be appreciably modified in desired directions. The salts are more stable than are the free bases as regards freedom from oxidation by air, etc. Any substantially non-toxic acid may be employed for preparing the salts. The base in appropriate organic solvent may be treated with a solution of the desired acid and the solvents then removed, or the base may be dissolved by shaking with an aqueous solution of the chemical equivalent of acid and the solvent then evaporated. In either case, the salt maybe further purified by crystallization from appropriate solvent or by precipitation from solution by addition of an appropriate liquid in which the salt is fairly insoluble.

Specific compounds in this series zene are added slowly to 23 g. of the acid chloride of carbazole-Z-carboxylic acid (prepared by the interaction of the acid and phosphorus pentachloride) in 200 cc. of benzene. To insure completion of the reaction, the mixture is heated for three hours on a water bath after which it is shaken with dilute hydrochloric acid. The aqueous layer is separated and made alkaline with sodium hydroxide. The precipitated p-diethylarninoethyl ester of carbazole-2-carboxylic acid is extracted with ether, the ethereal extract dried and then saturated with dry gaseous hydrogen chloride. The resulting precipitate is crystallized thrice from methyl alcohol to obtain the hydrochloride, melting at 195 C. The product is a local anesthetic. By neutralizing the free base with other acids besides hydrochloric, various salts may be obtained.

,B-diethylaminoethyl carbazole-B-carboxylate, prepared by the same method, melts at 127 C.

fl-diethylaminoethyl carbazole-4 carboxylate, prepared by the same method, was an oil. Its salts however were solids.

Substitution of the acid chloride of 5-ethyl carbazole-z-carboxylic acid in the example given above, yields by only slight modification of procedure, the p-diethylaminoethyl ester in good yield.

' 8-nitro carbazole-Z-carborqrlic acid p-diethylaminoethyl ester, prepared by essentially the same procedure, is dissolved in ethyl alcohol, concentrated hydrochloric acid is added and the mixture is shaken with an excess of granular tin until reduction of the nitro group to form the amino group is complete. The excess tin is filtered off, and the alcohol is distilled off. The remaining tin is removed as the sulfide with hydrogensulfide. The mixture is made faintly alkaline with sodium hydroxide and the precipitate is extracted with ether. The ether solution is dried and filtered with charcoal. Upon evaporating ofi the solvent the ester of B-amino carbazole-2-carboxylic acid is secured as a crystalline residue- It may be re-crystallized from suitable solvents. I

14 gm. of ,B-dibutylaminoethanol dissolved in benezene, are slowly added to a solution of 23 gm. of the acid chloride of carbazole-Z-carboxylic acid, similarly dissolved. After standing briefly,

the mixture is heated to insure completion of the reaction, cooled, and extracted with an excess of dilute hydrochloric acid. The aqueous layer is separated, filtered with charcoal, and made alkaline with sodium hydroxide. The liberated ester is extracted with ether, the ethereal solution is dried and filtered with charcoal. The ester may be converted to its hydrochloride with gaseous hydrogen chloride. By addition of ethereal solutions of appropriate organic acids in equivalent quantity, the material is converted to its organic salts. These are recovered by evaporating the ether and may be i e-crystallized from appropriate solvents.

'7-ethoxycarbazole-3-carboxylic acid (prepared by acetylation of 'Y-ethoxycarbazole and oxidation of, the acetyl group) is converted to the acid chloride with phosphorous pentachloride. 14 g. of c-diethylaminoethanol in benzene are added slowly to a solution of 27.3 g. of the above acid chloride similarly dissolved. The mixture is heated to insure completion of the reaction, cooled, and extracted with an excess of dilute hydrochloric acid. The aqueous layer is separated, filtered with charcoal and made alkaline ith sodium hydroxide. The precipitated ester is taken up in ether, the etheral solution dried and then saturated with hydrogen chloride. The crude p-diethylaminoethyl 7-ethoxycarbazole-3- carboxylate hydrochloride thus obtained is crystallized from suitable solvents. Alternatively, there may be added to the etheral solution of the base, its equivalent of sulfuric acid. After evaporation of the ether the sulfate of the ether is secured. This may be re-crystallized for further purification.

The foregoing specific examples have been given merely for the purpose of illustrating the invention and the means of practicing it, and it will be understood that substitution may be made and equivalent modifications employed by those skilled in the art without departing from the spirit and scope of my invention. No unnecessary limitations should, therefore, be understood therefrom, but the appended claims should be construed as broadly as permissible in view of the prior art.

I claim: 1. Anesthetic preparations comprising dialkylaminoalkanol esters of the group consisting of carbazole 2, 3 and 4 carboxylic acids and salts thereof of the formula 2 lcoowflmnmnoz where R is of the group consisting of H, methyl, ethyl,

propyl, butyl, amyl and benzyl,

R is of the group consisting of methyl, ethyl,

propyl, butyl, amyl and benzyl,

R is of the group consisting of H, NI-Iz, and CR and may be attached to any carbon of the carbazole nucleus other than that substituted by the carboxyl group,

R is of the group consisting of H, methyl, ethyl,

propyl, butyl, amyl and benzyl,

n is an integer from 1 to 4 (chain may be straight or branched).

' r 2. Anesthetic preparations comprising dialkylaminoalkanol esters of carbazole 3 carboxylic acids and salts thereof of the formula where R, R R R and n have the same significanoe as in claim 1 and where R may be attached to any carbon of the oarbazole nucleus other than 3.

3. Anesthetic preparations comprising dialkylaminoalkanol esters of carbazole 3 carboxylic acids of the formula where R, R R and n have the same significance as in claim 1, and where the OR. group may be attached to any carbon of the carbazole nucleus other than 3.

4. Anesthetic preparations comprising dialkyl-.

aminoalkanol esters of carbazole 3 carboxylic acids of the formula where R, R and n have the same significance as in claim 1.

6. An anesthetic preparation comprising the p-diethylaminoethyl ester of carbazole 3 carboxylic acid of the formula II 2 N/ cocomomMmm):

7. Anesthetic preparations comprising dialkylaminoalkanol esters of carbazole 3 carboxylic acids of the formula where R, R R R and n have the same significance as in claim 1 and where R may be attached 20 to any carbon of the carbazole nucleus other than 3.

ROBERT R. BUR'INER.

7 CERTIFICATE OF CO RRECI'ION. Patent No. 2,250,0Olp. July 22, 19in.

. ROBERT R. BURTNER.

It is hereby certified that error appears in the printed specification of the Above numbered patent requiring correction as follows; Page 2, second column, line 8, for the word "ether" second occurrence, read -ester--; and that the said Letters Patent should be read with this correction therein that the same may conform to the reoord of the case in the Patent Office.

Signed and sealed this 25rd day of September, A. D.. 19in.

Henry Van Arsdale, (Seal) Acting Commissioner of Patents. 

